1. Field of the Invention
The present invention relates to a thermoelectric conversion module and a method for manufacturing a thermoelectric conversion module.
Priority is claimed on Japanese Patent Application No. 2012-32491, filed on Feb. 17, 2012, the contents of which are incorporated herein by reference.
2. Description of Related Art
In the past, a thermoelectric material has been used for a variety of purposes in order to carry out conversion between heat and electric power. For example, a thermoelectric conversion module has been developed in which an n-type thermoelectric material and a p-type thermoelectric material are connected in series and are disposed side by side between facing substrates so that one substrate is used as a high-temperature portion, and the other substrate is used as a low-temperature portion. The thermoelectric conversion module is used for conversion of heat supplied to the thermoelectric conversion module from the high-temperature portion into electric power, cooling at the low-temperature portion through electric conducting, and the like.
In the above configuration, while the temperature at the high-temperature portion is varies, in order to use the thermoelectric conversion module in a temperature range exceeding the melting point of solder, a technique for manufacturing the thermoelectric conversion module, in which solder is not used, has been developed. For example, Japanese Unexamined Patent Application, First Publication No. 2004-273489 discloses a technique in which a thermoelectric element or the like is welded by coating conductive paste having fine metal particles with an average particle diameter of 1 to 10 nm dispersed in liquid on the thermoelectric element, an electrode sheet or the like, and then sintering the fine metal particles.
In the technique of the related art, it was not possible to configure a thermoelectric conversion module which was durable enough to withstand use in an operation condition of a large temperature difference between the high-temperature portion and the low-temperature portion. For example, in a case in which power is generated using a thermoelectric element, it is assumed that a thermoelectric conversion module is used in an environment in which the high-temperature portion becomes 300° C. or more, and the low-temperature portion becomes room temperature (approximately 25° C.). In such an environment, a large temperature difference is caused between the high-temperature portion and the low-temperature portion in the thermoelectric conversion module, and a large temperature difference is also caused between the thermoelectric element and an electrode. Generally, since the thermoelectric element and the electrode have totally different components, in an operation environment in which a large temperature difference is caused, the degrees of thermal expansion are significantly different at the thermoelectric element and the electrode, and a large thermal stress is caused between the thermoelectric element and the electrode. Therefore, even when a joining layer is formed using fine metal particles, breakage or the like of the joining layer occurs in the technique of the related art in which the mitigation of thermal stress is not assumed.